Switching device for lighting the interior of a motor vehicle

ABSTRACT

In a switching device for the interior lighting L of a motor vehicle, having a timing element R1 C1 which is controlled by a gate contact switch TK which is opened by closing a vehicle door and which sets on the interior lighting during a certain time lapse after closing the door, a second timing element R2 C2 is provided to be controlled by the closing of the gate contact switch TK and to set off the interior lighting L after a predetermined time interval, when the ignition switch ZS is open. Thereby, the discharge of the vehicle battery is prevented due to the interior lighting L when a door remains inadvertently open, but, when the ignition is turned on, the interior lighting L remains on if a door is open.

The invention relates to a switching device for lighting the interior ofa motor vehicle having an ignition switch.

Such circuits have the advantage that the seat belts can be put on andthe key inserted in the ignition lock or the driver's door locked fromthe outside while the interior lights are switched on. It is however adisadvantage that the battery of the vehicle may become discharged if adoor of the vehicle is inadvertently left open over a longer period oftime and for this reason the interior lights remain switched on by thedoor contact switch, which in this case is in the closed position.

It is an object of the invention to provide a switching device, withwhich discharging of the vehicle battery, when the door is left open forlong periods, is prevented.

This objective is accomplished by the distinguishing features describedbelow.

When the door is open (that is, when the door contacts are in the closedposition), the inventively provided second timing element switches offthe interior lighting after several minutes, however only if theignition switch is open and the engine thus is not running, since it isnormally not possible to discharge a battery when the engine is runningand it would be unacceptable that, when the is engine running and thevehicle thus normally is occupied, the interior lights go out when avehicle door is open for some time.

Preferably, the second timing element remains set through closing theignition switch is closed, so that, after the door is closed and theignition switched on, the interior lighting remains switched on evenwhen a vehicle door stays open for some time.

With a conventional delay circuit, the interior lighting, after the dooris closed, remains switched on through a transistor, whose base isconnected with the output of an operational amplifier, whose +ve inputis taken to a reference voltage and whose -ve input is at a potential,which is lower when the when the door contact switch is closed andhigher when the door contact switch is open, that its +ve input. Withsuch a circuit, the +ve input of an operational amplifier can beconnected to the output of a comparator, the -ve input of which sees areference voltage and the +ve input of which is brought by the secondtime element to a potential lower than that of its -ve input at aspecified time after the door contact switch is closed and to apotential higher than that of its -ve input by closing the ignitionswitch.

An example of the operation of the invention is described in thefollowing with reference to the drawing which shows a schematic diagramfor a preferred embodiment of the invention.

The interior light L of a motor vehicle is connected, on the one hand,to the positive pole of the vehicle battery and, on the other, can beconnected by manual switch S either directly (position 1) or throughrelaycontacts RK (position 2) to the negative pole, that is, to ground.In addition, switch S has an open position 0. The relay contacts RK areclosed when current is flowing in the coil of relay R. This coil isconnected, on the one hand, to the positive pole of the vehicle batteryand, on the other, through a transistor T to ground. The base oftransistor T is connected to the output of an operational amplifier OPwhose inverting (-) input is connected through a resistance R1 to thepositive pole and through a door contact switch TK, which is closed whenthe vehicle door is open, and two diodes D1 and D2 to ground. Inaddition,a capacitor C1 is arranged between the (-) input of theoperational amplifier OP and ground. The noninverting (+) input of theoperational amplifier is connected to a reference voltage node A, whichis formed by resistances R3 and R4, R5.

Resistance R1 and capacitor C1 form a first timing element, whichcontinuesto maintain the excitation of relay R over a predeterminedperiod of time after the door of the vehicle is closed, that is, afterthe previously closed door contact switch TK is opened. Through openingTK, the potentialat the (-) input of the OP is increased continuouslyfrom the value of the sum of the forward voltages of D1 and D2, that isfrom 1.4 V, while the (-) input is at the potential of, for example 8 V.With this arrangement, the base of transistor T is positive before andafter TK is closed, so that transistor T continues to drive light, whenmanual switch S is in position 2. If the voltage at the (-) input of OPgradually rises above the value of the potential of the (+) input due tothe charging of capacitor C1 through resistance R1, the output of theoperational amplifier OP and, with it, the base of transistor T areswitched to ground, as a result of which transistor T turns off, relay Rdrops out, relay contacts RK are opened and light L goes out.

If the door is opened, door contact TK is closed and the (-) input of OPisgrounded by diodes D1 and D2, as a result of which its potentialbecomes lower than the potential of the (+) input, so that its outputand, with it, the base of transistor T go high, the transistor isactivated turning light L on.

In order to prevent discharging of the vehicle battery throughcontinuous burning of light L when the door of the vehicle remains openfor a longer period of time, a second timing element R2, C2 is provided,which causes the circuit of relay R to be interrupted when a specifiedperiod of time has elapsed after the door is opened. For this purpose,the (+) input of the operational amplifier OP is connected with theoutput of the comparator K, the inverting (-) input of which isconnected with a reference voltage node B, which is formed byresistances R5 and R4, R3, and the noninverting (+) input of which isconnected to ground over resistance R2 of the second timing element, adiode D3 and the door contact switch TK, which is closed when the dooris open. Capacitor C2 of the second timing element is connected betweenthe (+) input of comparatorK and ground. If the door is opened, that is,if the door contact TK is closed, the +ve input of comparator Kinitially is at a higher potential than the (-) input due to the factthat capacitor C2 has previously been charged over the low resistance R6and the diode D4. This means that the output of the comparator is high.As capacitor C2 discharges through the high resistance R2, the potentialof the (+) input of comparator K falls off continuously, until the valueof the capacitor voltage of C2 has dropped below the potential of the(-) input, as a result of which the output of the comparator and, withit, the (+) input of the operational amplifier OP, which is decoupledover high resistance R10 from the reference voltage source at node A,are connected to ground. As a result, the potential of the (+) input ofthe operational amplifier OP, whose value is less than 0.7 V, is lowerthan the potential of the (-) input, which lies at about 1.4 V becauseof the voltage drop of the diodes D1, D2in the forward direction.Consequently the output of the operational amplifier OP and, with it,the base of transistor T are connected to ground, transistor T turnsoff, relay R drops out, relay contacts RK are opened and light L goesout. The second timing element R2, C2 has a delay time of, for example,4 minutes, while the delay time of the first time element R1, C1 is, forexample, 30 seconds.

In order to prevent light L from being turned off when a vehicle door isopen over a longer period of time with the ignition switched on, thatis, with the engine running, the (+) input of comparator K can also beconnected through ignition switch ZS through the low resistance R7 andthediode D5 directly to the positive pole. Through closing ZS, thedischargingof capacitor C2 stops due to the high resistance R2, that is,the (+) inputof comparator K remains at a higher potential than the (-)input, so that the connection between the output of comparator K and the(+) input of theoperational amplifier OP remains high and the conductingstate of transistor T is maintained.

With a switch ZS1, which is closed when the ignition is turned on, the(-) input of the operational amplifier OP can be connected through a lowresistance R8 and a diode D6 to the positive pole of the vehiclebattery. Thus, with the door closed and thus the door contacts TK open,light L goes out immediately when the ignition is turned on, since thepotential of the (-) input then is higher than the potential of the (+)input and therefore the output of the operational amplifier OP and, withit, the base of transistor T are connected to ground. For vehicles witha central locking device, a switch ZV is arranged in parallel withswitch ZS1. When the central locking device is activated, switch ZV isclosed and connects the (-) input of the OP over a low resistance R9 anda diode D7 with the positive pole of the vehicle battery. This causeslight L to go out immediately almost. It is possible to delay turningoff the light after ZS1 or ZV is closed at will from fractions of asecond to several seconds by selecting appropriate values forresistances R8 and R9.

Many modifications of the examples of the operation shown are of coursepossible without departing from the scope of the invention. It is, forexample, well known to those skilled in the art that the same functionscan be carried out with an integrated twin comparator component, a dualoperational amplifier circuit or also with TTL Schmitt triggers or CMOStechnology and that, instead of the RC element, other electroniccomponents, for example, a flip-flop, can be used as time element. Ifthe load is light, that is, if the interior lighting consists of fewlights, it is possible to do without relay R and to connect the emitterof transistor T directly to contact 2 of the manual switch S.

What is claimed is:
 1. Switching device used in the interior lighting ofa motor vehicle provided with an ignition lock and a battery, with atiming element that is controlled by a door contact switch, which isopened when a door of the vehicle is closed, and that permits theinterior lighting to be left switched on for a first specified timeafter the door is closed, characterized in that a second timing element(C2 R2) is provided, which is controlled by closing the door contactswitch (TK) and which turns off the interior lighting (L) after a secondspecified time when the ignition switch (ZS) is open and the doorcontact switch (TK) remains closed wherein said second specified time isselected to prevent discharge of said battery to a level hinderingignition of the engine of said motor vehicle.
 2. Switching device asdefined in claim 1, wherein the second timing element (R2 C2) isde-activated by closing the ignition switch (ZS).
 3. Switching device asdefined in claims 1 or 2, in which the interior illumination is switchedon by a transistor, the base of which is connected to the output of anoperational amplifier, the positive input of which amplifier isconnected to a first reference voltage and the negative input of which,with the door contact switch open and after said first specified time,is at a higher potential than said positive input, wherein the positiveinput is brought to a lower potential than the potential of the negativeinput by the second timing element (R2 C2) when said second specifiedtime has elapsed and to a higher potential than the potential of thenegative input by opening the door contact switch (TK) or by closing theignition switch (ZS).